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1. General Principles & Basic Science MCQs

Practice Set 149 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 2961

Topic: 1. General Principles & Basic Science

You are planning an osteotomy to correct a diaphyseal tibial deformity. You identify the CORA, but due to poor skin quality at that level, you decide to perform the osteotomy proximal to the CORA. If you place your hinge at the site of the osteotomy (away from the CORA), what will be the geometric result according to Paley's principles?

. Pure angular correction with collinear axes
. Realignment of axes by angulation and associated translation, making the axes collinear
. The mechanical axes will become parallel but not collinear, creating a new translational deformity
. The joint orientation angles will become permanently distorted
. Correction of length discrepancy without angular correction

Correct Answer & Explanation

. The mechanical axes will become parallel but not collinear, creating a new translational deformity

Explanation

Paley's Osteotomy Rule 3 states that if the osteotomy and the hinge are both placed away from the CORA, the mechanical axes of the proximal and distal segments will become parallel but not collinear, creating a secondary translation deformity.

Question 2962

Topic: 1. General Principles & Basic Science

In a structurally normal lower extremity, what is the expected relationship between the anatomic axis and the mechanical axis of the femur?

. They are exactly collinear and parallel.
. The anatomic axis diverges from the mechanical axis by approximately 5 to 7 degrees of valgus.
. The anatomic axis diverges from the mechanical axis by approximately 5 to 7 degrees of varus.
. They intersect at the center of the femoral diaphysis.
. The mechanical axis passes through the greater trochanter, while the anatomic axis passes through the center of the femoral head.

Correct Answer & Explanation

. The anatomic axis diverges from the mechanical axis by approximately 5 to 7 degrees of valgus.

Explanation

The mechanical axis of the femur runs from the center of the femoral head to the center of the knee. The anatomic axis runs down the center of the femoral diaphysis, resulting in a normal divergence of approximately 5 to 7 degrees.

Question 2963

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis utilizing an Ilizarov frame, a 'latency period' is recommended before initiating distraction. What is the primary biological purpose of this latency period?

. To allow the formation of woven bone across the entire gap prior to lengthening
. To allow the acute inflammatory phase to subside and early soft callus to populate the osteotomy gap
. To prevent pin site infections from early mechanical sheer
. To allow complete endochondral ossification of the fracture hematoma
. To ensure cortical remodeling of the adjacent diaphyseal bone

Correct Answer & Explanation

. To allow the acute inflammatory phase to subside and early soft callus to populate the osteotomy gap

Explanation

A latency period of 7 to 10 days is standard to allow the initial fracture hematoma to organize into a soft callus rich with mesenchymal stem cells and vascularity. This provides the optimal biological environment for membranous ossification under tension.

Question 2964

Topic: 1. General Principles & Basic Science

A patient with an established uniapical varus deformity of the proximal tibia is undergoing an opening wedge osteotomy. To adhere to Osteotomy Rule 1 and avoid any unwanted translation, where must the hinge of the opening wedge be positioned?

. On the concave (medial) cortex at the level of the CORA
. On the convex (lateral) cortex at the level of the CORA
. At the center of the tibial diaphysis exactly 1 cm distal to the CORA
. At the mechanical axis line 2 cm proximal to the CORA
. On the medial cortex 2 cm proximal to the CORA

Correct Answer & Explanation

. On the convex (lateral) cortex at the level of the CORA

Explanation

To execute an opening wedge osteotomy under Rule 1, the hinge must be placed on the convex side of the deformity (lateral cortex for a varus deformity) exactly at the level of the CORA.

Question 2965

Topic: Biology, Genetics & Bone Healing

A patient is undergoing distraction osteogenesis with a Taylor Spatial Frame. Radiographs show the typical 'zonal' appearance of the regenerate. What is the predominant composition of the central radiolucent 'Fibrous Interzone' (FIZ)?

. Type II collagen with endochondral ossification
. Type I collagen bundles oriented longitudinally along the vector of distraction
. Avascular necrotic bone and dense scar tissue
. Woven bone undergoing rapid osteoclastic resorption
. Cartilaginous anlagen without vascular ingrowth

Correct Answer & Explanation

. Type I collagen bundles oriented longitudinally along the vector of distraction

Explanation

Distraction osteogenesis occurs primarily via membranous ossification. The central radiolucent FIZ is composed predominantly of Type I collagen organized in bundles parallel to the vector of distraction, serving as a scaffold for mineralization.

Question 2966

Topic: 1. General Principles & Basic Science

You are applying a circular external fixator to the proximal tibia. When placing a transverse wire through the fibular head to capture the proximal tibiofibular joint, which major neurovascular structure is at greatest risk if the wire is placed too far posterior?

. Popliteal artery
. Tibial nerve
. Common peroneal nerve
. Anterior tibial artery
. Saphenous nerve

Correct Answer & Explanation

. Common peroneal nerve

Explanation

The common peroneal nerve courses around the fibular neck, just posterior and inferior to the fibular head. Placing wires too far posterior in this region places the nerve at significant risk of injury.

Question 2967

Topic: 1. General Principles & Basic Science

You are correcting a severe uniapical valgus deformity of the tibia. You decide to place the osteotomy exactly at the CORA, but due to adjacent soft tissue compromise, you place the hinge strictly on the mechanical axis line 3 cm distal to the CORA. What is the expected outcome of this correction?

. Collinear alignment of the axes with no translation
. Realignment of axes by angulation and associated translation, making the axes collinear
. Parallel but not collinear mechanical axes, creating a new translation deformity
. Complete failure of the osteotomy to open due to hinge impingement
. A primary rotational deformity secondary to off-axis hinging

Correct Answer & Explanation

. Realignment of axes by angulation and associated translation, making the axes collinear

Explanation

This describes Osteotomy Rule 2. When the hinge is on the CORA transverse bisector line (or the axes lines themselves depending on the exact geometry, essentially when the hinge is not at the CORA but the osteotomy is at the CORA), correction occurs via angulation and translation, resulting in collinear mechanical axes.

Question 2968

Topic: 1. General Principles & Basic Science

When calculating the Magnitude of Deformity in a patient with a uniapical varus tibia, you identify the intersection of the proximal and distal mechanical axes. The angle formed at this intersection is exactly equal to the angle required for complete correction. What is this intersection point called?

. The Joint Line Convergence Angle (JLCA)
. The Mechanical Axis Deviation (MAD)
. The Center of Rotation of Angulation (CORA)
. The Bisector Line
. The Virtual Hinge

Correct Answer & Explanation

. The Center of Rotation of Angulation (CORA)

Explanation

The intersection of the proximal and distal mechanical (or anatomical) axes of a deformed bone defines the Center of Rotation of Angulation (CORA). The angle measured at this intersection is the magnitude of the angular deformity.

Question 2969

Topic: 1. General Principles & Basic Science

During a tibial lengthening procedure of 6 cm at a rate of 1 mm per day, the patient complains of severely increasing pain out of proportion around week 3, accompanied by an inability to actively dorsiflex the great toe and decreased sensation in the first web space. What is the most likely etiology?

. Pin tract infection of a proximal wire
. Normal physiological stretching of the sural nerve
. Deep vein thrombosis
. Tethering or stretch injury to the deep peroneal nerve
. Premature consolidation of the regenerate

Correct Answer & Explanation

. Tethering or stretch injury to the deep peroneal nerve

Explanation

Severe pain and new neurologic deficits (weakness in EHL, numbness in the first web space) during a significant distraction indicate stretch-induced nerve injury to the deep peroneal nerve. The distraction must be stopped or reversed immediately.

Question 2970

Topic: 1. General Principles & Basic Science

A surgeon plans a tibial deformity correction. The Center of Rotation of Angulation (CORA) is located at the diaphyseal-metaphyseal junction. The osteotomy is performed in the mid-diaphysis due to poor skin quality, but the hinge of the external fixator is placed exactly over the CORA. According to Paley's osteotomy rules, what will be the resulting alignment?

. Collinear realignment with no translation
. Collinear realignment with translation at the osteotomy site
. Non-collinear alignment with a new mechanical axis deviation
. Parallel translation without angular correction
. Complete failure of angular correction

Correct Answer & Explanation

. Collinear realignment with translation at the osteotomy site

Explanation

Paley's Osteotomy Rule 2 states that if the osteotomy is located outside the CORA but the hinge is placed on the CORA, the mechanical axes will fully realign, but expected translation will occur at the osteotomy site.

Question 2971

Topic: 1. General Principles & Basic Science

When utilizing a hexapod circular external fixator (e.g., Taylor Spatial Frame) for lower extremity deformity correction, which of the following best defines the 'mounting parameters'?

. The lengths of the 6 struts prior to deformity correction
. The precise spatial relationship between the reference ring and the origin of the deformity
. The measurement of the deformity in the coronal and sagittal planes
. The daily rate and rhythm of the strut adjustments
. The anatomical mechanical axis deviation measured on preoperative standing radiographs

Correct Answer & Explanation

. The precise spatial relationship between the reference ring and the origin of the deformity

Explanation

Mounting parameters define the exact spatial position (axial, coronal, and sagittal translation/rotation) of the reference ring relative to the origin of the deformity. Accurate mounting parameters are essential for the software to generate a correct strut adjustment prescription.

Question 2972

Topic: 1. General Principles & Basic Science

A 14-year-old male is undergoing a 4 cm proximal tibial lengthening using a circular frame. Two weeks into the distraction phase, he develops new-onset weakness in great toe extension and numbness over the first dorsal web space. What is the most appropriate initial management?

. Perform an acute common peroneal nerve release
. Increase the distraction rate to relieve tension
. Halt distraction and apply a dorsiflexion splint
. Remove the external fixator immediately
. Prescribe high-dose oral corticosteroids

Correct Answer & Explanation

. Halt distraction and apply a dorsiflexion splint

Explanation

The patient has developed a common peroneal nerve stretch injury, a known complication of proximal tibial lengthening. Initial management is to immediately halt distraction, apply a splint to prevent equinus contracture, and observe for recovery before considering decompression.

Question 2973

Topic: 1. General Principles & Basic Science

A surgeon corrects a valgus tibial deformity by placing the osteotomy and the hinge of the external fixator exactly at the Center of Rotation of Angulation (CORA). Which of the following accurately describes the geometric outcome according to Paley's principles?

. The bone ends will translate but not angulate
. The bone ends will angulate and fully realign without translation
. The bone ends will angulate with significant expected translation at the osteotomy
. A new secondary Center of Rotation of Angulation will be created
. The mechanical axis deviation will increase proportionally to the angle

Correct Answer & Explanation

. The bone ends will angulate and fully realign without translation

Explanation

Paley's Osteotomy Rule 1 states that if both the osteotomy and the correction hinge are located exactly at the CORA, the mechanical axes will realign collinearly without any translation at the osteotomy site.

Question 2974

Topic: 1. General Principles & Basic Science

According to Paley's Rule 1 of deformity correction, what is the expected geometric outcome when both the osteotomy and the hinge of the corrective device are placed exactly at the Center of Rotation of Angulation (CORA)?

. Angulation combined with translation
. Translation without angulation
. Pure angulation without translation
. Pure lengthening without angulation
. Shortening with compensatory translation

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Paley's Rule 1 states that when the osteotomy and the hinge of the corrective device are both located at the CORA, the deformity corrects by pure angulation without any translation of the bone ends.

Question 2975

Topic: 1. General Principles & Basic Science

A 45-year-old patient has a distal femoral deformity. Preoperative planning determines that the osteotomy must be performed proximal to the CORA due to poor skin quality at the true apex. To achieve colinear realignment of the proximal and distal anatomic axes without creating a secondary deformity, where MUST the hinge (axis of rotation) be placed?

. At the level of the planned osteotomy
. At the center of the knee joint
. Exactly at the CORA
. Proximal to the osteotomy
. Distal to the CORA

Correct Answer & Explanation

. Exactly at the CORA

Explanation

According to Paley's Osteotomy Rule 2, if the osteotomy is performed at a different level than the CORA, the axis of rotation (hinge) must still be placed at the CORA. This results in angulation with simultaneous translation, effectively realigning the axis.

Question 2976

Topic: 1. General Principles & Basic Science

A surgeon is evaluating a 30-year-old with a multi-apical curved diaphyseal tibial deformity. When performing the graphic analysis, the proximal and distal anatomic axes intersect to form a single apparent CORA that falls entirely outside the bone. What is the most appropriate approach to correct this specific deformity?

. A single osteotomy at the exact intersection of the axes (the apparent CORA)
. Two separate osteotomies corresponding to each distinct apex of the curve
. A single opening wedge osteotomy at the distal metaphysis
. An intra-articular osteotomy to realign the joint surface
. A purely translational osteotomy without angulation

Correct Answer & Explanation

. Two separate osteotomies corresponding to each distinct apex of the curve

Explanation

Multi-apical or curved diaphyseal deformities often have an apparent CORA that falls outside the bone. These are best treated with multiple osteotomies at the true apices of the deformity to accurately restore the mechanical axis.

Question 2977

Topic: 1. General Principles & Basic Science

What is the normal relationship between the anatomic and mechanical axes of the femur in the coronal plane, and what is the typical magnitude of the Anatomic-Mechanical Angle (AMA)?

. They are parallel and do not intersect
. They intersect at the knee joint at an angle of 12-15 degrees
. They intersect at the knee joint at an angle of 5-7 degrees
. They intersect at the femoral head at an angle of 5-7 degrees
. They are identical and colinear in the coronal plane

Correct Answer & Explanation

. They intersect at the knee joint at an angle of 5-7 degrees

Explanation

In the femur, the mechanical axis (from femoral head center to knee center) and the anatomic axis (down the medullary canal) intersect at the knee joint. This forms the anatomic-mechanical angle (AMA), which normally ranges from 5 to 7 degrees.

Question 2978

Topic: 1. General Principles & Basic Science

In lower extremity deformity planning using the center of rotation of angulation (CORA) method, what happens to the measured magnitude of the deformity angle if it is measured at points along the anatomic axis proximal or distal to the actual CORA?

. It increases as you move away from the CORA
. It decreases as you move away from the CORA
. It remains geometrically constant everywhere between the intersecting axes
. It becomes falsely negative distal to the CORA
. It becomes zero outside the metaphyseal region

Correct Answer & Explanation

. It remains geometrically constant everywhere between the intersecting axes

Explanation

The magnitude of the angulation deformity is geometrically identical at any point along the two intersecting lines (axes) that form the CORA. While the CORA defines the physical location of the apex, the angular magnitude itself is constant between the intersecting lines.

Question 2979

Topic: 1. General Principles & Basic Science

A 30-year-old patient presents with a lower extremity deformity. The full-length standing radiograph below shows a limb with the mechanical axis passing significantly lateral to the center of the knee joint. Based on the principles of frontal plane deformity correction, what type of deformity is depicted, and what is its primary biomechanical implication?

. A. Varus deformity, leading to increased load on the medial compartment.
. B. Valgus deformity, leading to increased load on the medial compartment.
. C. Varus deformity, leading to increased load on the lateral compartment.
. D. Valgus deformity, leading to increased load on the lateral compartment.
. E. Recurvatum deformity, leading to increased load on the posterior compartment.

Correct Answer & Explanation

. D. Valgus deformity, leading to increased load on the lateral compartment.

Explanation

Correct Answer: DThe image shows the mechanical axis passing lateral to the center of the knee, which is characteristic of a valgus deformity. The text states: 'Conversely, a valgus deformity overloads the lateral compartment.' Therefore, a valgus deformity leads to increased load on the lateral compartment.Incorrect Options:A. Varus deformity, leading to increased load on the medial compartment:This describes a varus deformity, but the image clearly shows a valgus deformity (mechanical axis lateral to the knee).B. Valgus deformity, leading to increased load on the medial compartment:While the image shows a valgus deformity, a valgus deformity overloads thelateralcompartment, not the medial compartment.C. Varus deformity, leading to increased load on the lateral compartment:This is incorrect on both counts; the image is valgus, and varus overloads the medial compartment.E. Recurvatum deformity, leading to increased load on the posterior compartment:Recurvatum is a sagittal plane deformity (hyperextension of the knee), not a frontal plane deformity, and is not depicted in the image or discussed in the context of frontal plane loading in the text.

Question 2980

Topic: 1. General Principles & Basic Science

A 38-year-old male presents with chronic right knee pain and a noticeable bowing of his leg. A full-length weight-bearing anteroposterior radiograph is obtained, as shown below. The mechanical axis (dotted line) passes significantly medial to the center of the knee joint. Which of the following statements accurately describes the biomechanical implications of this finding?

. The patient has a valgus deformity, leading to increased loading of the lateral compartment.
. The mechanical axis deviation (MAD) is negative, indicating a lateral compartment overload.
. The patient has a varus deformity, resulting in a positive MAD and increased medial compartment stress.
. The mechanical axis deviation (MAD) is within the normal 8 mm zone, suggesting no significant structural deformity.
. The deformity is primarily located in the proximal tibia, causing the observed knee alignment.

Correct Answer & Explanation

. The patient has a varus deformity, resulting in a positive MAD and increased medial compartment stress.

Explanation

Correct Answer: CThe image clearly shows the mechanical axis passing medial to the center of the knee joint. According to the case material, this indicates a varus (bowlegged) deformity. A varus deformity results in a positive Mechanical Axis Deviation (MAD), which pathologically overloads the medial compartment of the knee, leading to accelerated medial compartment osteoarthritis. Therefore, option C is correct.Option A is incorrect because a valgus deformity (knock-kneed) would have the mechanical axis passing lateral to the knee center, overloading the lateral compartment. Option B is incorrect because a negative MAD corresponds to a valgus deformity. Option D is incorrect as the mechanical axis is clearly significantly deviated medial to the knee, well outside the normal 8 mm zone. Option E is incorrect because while a tibial deformity can contribute to varus, the image and description specifically point to the overall limb alignment and the implications of the mechanical axis passing medial to the knee, which is characteristic of a varus deformity regardless of the specific bone of origin without further joint angle measurements.

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